1. Field of the Invention
The present invention relates to ink tanks used in inkjet recording, and more particularly relates to an ink tank having an inner flexible ink containing portion for storing liquid such as ink and an outer casing for protecting the containing portion.
2. Description of the Related Art
An ink tank used in inkjet recording is required to produce an adequate negative pressure so as to feed liquid to a recording head which discharges liquid such as ink. Moreover, an ink tank, which is mounted on a carriage of a recording apparatus and which is detachable together with a recording head from the recording apparatus, is required to have a large ink-storing capacity, a small number of components, and a simple structure, in addition to having recyclable components.
To solve these problems, the same assignee disclosed an innovative liquid container, which is formed by blow molding, in U.S. Pat. No. 5,975,330. The liquid container has an outer wall having an atmospheric-air communicating portion and an approximate polygonal or prism-like shape, an inner wall which has outer surfaces substantially the same as or similar to inner surfaces of the outer wall and which forms a liquid containing portion for storing liquid therein, and a liquid feeding port. The liquid container is constructed such that the thickness of the inner wall is greater at the central part of each surface thereof than at the periphery of the surface (i.e., at corners and vertices of the polygon), and the inner and outer walls are separable from each other. In the liquid container, as liquid is being guided out from the liquid container, the largest surfaces of the inner wall which form a part of the polygon are first separated from the outer wall, and the corners of the inner wall remain attaching to the corresponding corners of the outer wall until the mutually opposing surfaces of the inner wall contact each other, thereby allowing the liquid ink container to produce a stable negative pressure.
However, depending on the kind of resin material used for the inner wall or when the inner wall is very thin, there is a risk in that a desired negative pressure is not obtained because a produced negative pressure is too small, or the liquid is not smoothly guided out from the containing portion because a part of the inner wall in the vicinity of the liquid feeding port is deformed.
It is an object of the present invention to provide an ink tank which addresses the foregoing problems and which produces a stable negative pressure and feeds liquid over a large range of thicknesses of the inner wall and with a variety of different kinds of resin material used for the inner wall.
To achieve the above objects, an ink tank according to the present invention comprises an inner wall forming a liquid containing portion for storing liquid; an outer wall, having inner surfaces whose shapes are substantially the same as those of outer surfaces of the inner wall, comprising at least one atmospheric-air communicating portion for introducing atmospheric air into a space between the inner wall and the inner surfaces of the outer wall; and a liquid feeding port for feeding liquid in the liquid containing portion to the outside. The inner wall is separable from the outer wall as the liquid is being guided out from the liquid feeding port. The ink tank further comprises a first region in which the inner and outer walls are bonded to each other and are separable from each other by an external force; and a second region, next to the first region, in which the inner and outer walls are bonded to each other and a larger external force is needed to separate the inner wall from the outer wall than in the first region. As the liquid is being guided out, the inner wall separates from the outer wall first in the first region and then in the second region.
According to the foregoing ink tank, since a deformable region of the inner wall which is deformed as ink is being guided out can be freely set, the liquid feeding port is not blocked by the deformed inner wall. Also, since the area of the deformable region increases as the ink is being guided out, the negative pressure in the ink tank varies in a predetermined range as the ink is being guided out, thereby allowing the ink tank to produce a stable negative pressure.
Another ink tank according to the present invention comprises an inner wall having an approximate polygonal or prism-like shape and forming a liquid containing portion for storing liquid; an outer wall, having inner surfaces whose shapes are substantially the same as those of outer surfaces of the inner wall, comprising at least one atmospheric-air communicating portion for introducing atmospheric air into a space between the inner wall and the inner surfaces of the outer wall; and a liquid feeding port for feeding liquid in the liquid containing portion to the outside. The inner wall is separable from the outer wall as the liquid is being guided out from the liquid feeding port. Also, the liquid feeding port is disposed on a surface of the inner wall except the largest-area surface of the same. In addition, a thickness distribution of each largest-area surface of the inner wall varies continuously so as to become larger from a position remote from the liquid feeding port toward the liquid feeding port.
According to the foregoing ink tank, since the separation of the inner wall begins to occur from a portion of the inner wall far away from the ink feeding port as the ink is being guided out, the liquid feeding port is not blocked by the deformed inner wall regardless of the kind of resin. Also, the thickness distribution determines the order of deforming portions of the inner wall, thereby allowing the ink tank to produce a stable negative pressure.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.